PROJECT SUMMARY This proposal will facilitate the principal investigator's career goals of advancing the understanding of the inherited basis for lipid traits and myocardial infarction (MI) and applying this understanding to the prevention of disease in patients. Building on his extensive research experience, the proposal will train him in the use of complementary approaches-human genetics of complex cardiovascular traits, and the use of mouse models and embryonic stem cells for functional validation of genes associated with these traits-to achieve a biological understanding of the results of genome-wide association studies (GWAS). It will also provide him with didactic training in statistical genetics, genetic and genomic methods, experimental biology, and research ethics. Finally, it will promote his transition to an independent research position and provide him a robust scientific foundation from which to apply for R01-level funding. The principal investigator will be able to take advantage of an absolutely unique environment with diverse strengths in animal models of cardiovascular disease (Massachusetts General Hospital Cardiovascular Research Center), cardiovascular genetics and genomics (Broad Institute of MIT and Harvard, Massachusetts General Hospital Center for Human Genetic Research), and stem cell biology (Massachusetts General Hospital Cardiovascular Research Center, Harvard Stem Cell Institute) to complete the proposed work. The rationale for the proposed research plan is that the discovery of new and effective treatments for human cardiovascular diseases requires the identification and validation in humans of novel disease mechanisms. Recently, studies of genomic variation entered a new phase, in which unbiased GWAS studies can identify novel genetic contributors to common diseases. In the last two years, more than fifty new and reproducible genomic loci were discovered contributing to lipid levels, MI, and type 2 diabetes. As promising as these observations may be, much work will be needed to convert novel associations into therapies. A key step is to identify the causal DNA variants in the mapped loci. Many loci contain multiple genes; other loci contain no known genes, suggesting that they may act in trans on genes outside of the loci. Thus, there is a need to unambiguously identify the causal gene(s) regulated by each locus. Finally, there is a need to address the mechanisms by which DNA variants in loci affect the causal genes. In short, a path must be blazed from genomic localization to new mechanistic insights. This proposal explores such a path for new genetic loci identified for low-density lipoprotein cholesterol (LDL- C) and MI. In preliminary studies, GWAS for LDL-C and MI and have identified single nucleotide polymorphisms (SNPs) in a locus on chromosome 1p13.3 that is robustly associated with LDL-C-more strongly than any other locus in the genome-very small LDL (vsLDL) particle concentration, and MI. Individuals who carry two copies of the major alleles of these SNPs have 16 mg/dl higher LDL-C, 40% higher vsLDL levels, and 18% greater risk of MI when compared with homozygotes for the minor alleles. The associated genomic interval on 1p13.3 spans ~100 kilobases (kb) and harbors four genes-CELSR2, PSRC1, MYBPHL, SORT1-with no established links to LDL-C regulation. The proposal's core questions are: (1) which 1p13.3 DNA variants contribute to LDL-C, vsLDL, and MI, (2) which 1p13.3 genes contribute to LDL-C, vsLDL, and MI, and (3) by what mechanisms do the DNA variants affect gene function? Genetic fine-mapping, gene resequencing, gene knockdown and overexpression in mice, and experiments in human embryonic stem cells will be used to answer these questions. Success should result in precise definition of a novel causal gene(s) and regulatory mechanism and thereby provide a potential new target for the treatment of dyslipidemia and prevention of MI.